
theorem Th533:
Sum digits(2040,10) = 6
proof
  thus Sum digits(2040,10) = Sum <%0,4,0%>+Sum <%2%> by Th532,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%0%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%0%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 4 + 0) + Sum <%2%> by AFINSQ_2:53
  .= 4 + 2 by AFINSQ_2:53
  .= 6;
end;
